Process of making a heat exchanging element



June 20,1939. A. J. BERG ET AL 2,162,694

PROCESS OF MAKING A HEAT EXCHANGING ELEMENT Filed Aug. 4, 1937 ms ES wemo. m Him IR A H L0 J Patented June 20, 1939 PATENT OFFICE Alfred J.

Application August 4,

2 Claims.

PROCESS OF MAKE??? A HEAT EXCHANGING MENT Berg, Portsmouth, N. IL, andJohn 0.

Huse, United States Navy 1937, Serial No. 157,380

(Granted under the act of March 3, 1883, as

amended April 30,

The usual heat exchanging element comprises a tube or other hollow orsolid body having one or more ribs projecting from the exterior surfacethereof.

ties and problems in an inexpensive and durable manner resulting ina-product that is neat and well finished as well as of great efliciencyin its heat exchanging capacity and. of substantially lesser weight andcost without detracting from the strength of the resulting product, orthe impairment ofits resistance to corrosion or other injurious actionof the elements.

Our product and method is illustrated in the accompanying drawing inwhich Fig. 1 is a side elevation view of a strip of metal which is to beconverted into a heat exchanger rib or ribs together with asideelevation view of the apparatus for practicing our method of forming theinner edge of such rib whichis to contact with the outer surface of theheat exchanging element or body;

Fig. 1a is an enlarged central vertical sectional view of a portion ofthe outer edge of the knurling wheel shown in Fig. 1;

Fig. 2 is a perspective view of a short broken- 40 off portion of theflat straight rib forming strip after the same has been helically formedabout, and for clarity removed from, the heat exchanger element or body;1

Fig. 3 is a plan view of a broken-away portion of a helically ribbedheat exchanger element or body in which the rib supporting and heattransfer bond increasing feet are partially formed;

Fig. 3a is an end view of a portion of the structure shown in Fig. 3;

Fig. 4 is a view similar to Fig. 3 but showing the rib supporting andheat transfer bond increasing feet in a more finished form;

Fig. 4a is an end view, similar to Fig. 3a, of an end view of a. portionof the structure shown in Fig. 4;

The body or its content is usually at 6 one temperature while the fluidin contact with;

the exterior surface of the body and ribs is at a Fig. 5 is a. view;similar to Fig. 4 but, showing the rib supporting and heat transfer bondincreasing feet in their finished form;

Fig. 5a is an end view similar to Fig. 4a, of the structure shown inFig. 5.

In the drawing, in which like characters of reference indicate the sameparts, It represents the rib material which is in the form of a flatstrip of metal of the thinness and width and character of metal desired.This strip I0 is first run edgewise between a stationary support II anda rotatable wheel I2. The support II is provided with a groove in itsside adjacent wheel I2, in which groove the strip I0 issupported uponone of its edges as well as upon its opposite sides by said groove; saidgroove being wide enough to freely receive the strip Ill and of a depthsuch that the opposite edge of strip III extends but slightly from theadjacent surfaces of the support I I. The wheel I2 is provided on itsperiphery' with a plurality of knurling teeth I3 which engage theexposed edge of the strip III which projects beyond the depth of thenotch in support II in which the strip I0 slides. The lateral walls ofthis notch insure the strip being held in upright engagement with thetooth periphery of the wheel I2, while the bottom of said notch insupport II maintains strip In in its desired engagement with the toothedperiphery of wheel I2. When the end of a strip I0 is inserted into thegroove in support II and wheel I2 is rotated manually or by power, theteeth I3 on the periphery of wheel I2 will form alternate projections I4and intervening spaces I5 in the edge of strip II in engagement with thenotched periphery of wheel I2. In such knurling the metal of strip I I,that was formerly in the spaces I5, will be cold worked by the knurlingteeth I3 into and increase the height of the adjacent projections I4.

The width of the groove in support II which receives the strip I0 may beadjustable to accommodate different thicknesses that may be desired forthe metal of the strip III, while the bottom of said groove in support II, which bears against one edge of strip Ill and the periphery of wheelI2 may be relatively adjusted to accommodate different desired widths ofstrips I0. Said adjustments may be made by the plurality of bolts I6 inthe support I I, or otherwise as may be desired.

Preferablyv secured to support II, and to the side of wheel I2 oppositethat from which the strip I0 is to be moved into engagement with wheelI2, is a foot I! which is provided with a cam surface I8 whichterminated adjacent wheel l2 with a bevelled surface I9. These surfacesl8 and I9 merge into each other and are adapted to engage and blunt orflatten the peaks of projections l4 formed upon an edge of strip III asaforesaid, the thrust of said flattening being borne by the support IIand its foot I! which is attached thereto by a suitable shank orotherwise.

As the strip comes from the successive and continuing knurling andflattening operations, the flattened v. surface adjacent its end isassociated with and secured by solder or otherwise to the outer surfaceof a tubular or other shaped body 20 which may be hollow, saidassociation preferably being with an initial portion of the edge ofstrip it, after the same has been knurled, and the knurled projectionsl4 flattened at least in part, engaging an outer surface of the tube orbody 20, with the sides of strip l0 extending at an angle, which may bea right angle, from thetube or body 20.

The strip I0 is then progressively bent edgewise about, or otherwise,into conformation with the surface of the tube or body 20. This edgewisebending progresses from said initial securement, and preferably extendsthroughout the length of the association of the strip ill with thesurface of the tube or body 20. Such pressure is preferablyprogressively and successively applied throughout the length of thestrip Ill being conformed into continuous engagement with the surface ofthe-tube or body 20. Such successivepressure applications not onlyconform by stages the cold worked edge of the strip ID to the surface oftube or body 20, but also progressively further flatten the adjacentsurface of projections 2| into ncontact with the surface of the tube orbody 20.

The strip II], for greater strength, as well as heat exchangerefficiency, is preferably cold rolled or otherwise cold worked. Thiscold working increases the strength of the strip It as well as its heatexchanging capacity or efficiency.

This enables the strips. to be employed of much thinner as well as widermetal than has been heretofore foundpossible' as well as practicable,The thinner the strips l0, and within limits the-wider they are, thegreater the increase in lightness as well as the heat exchangercapacityor efficiency ofthe tube or body 20 provided with the strips II)in the form of a rib or ribsextending from the surface of the tube orbody 20, and also the greater the reduction in the cost of the resultingproduct. This is true because the thinner thestrips are the lesser willbe the weight and cost of the resulting product. The thinner and widerare said strips III the larger is the area of their external surfacescompared to the cross-section of the metal of the strips l0.Furthermore, the thinner 'and wider are such strips l0 thegreater is thenumber of such strips that may be placed upon or about the surface of agiven length and diameter of tube or body 20 with the required,

preferably uniform, space between the strips In on the finished product.

A further economy in weight and cost, without impairment of its strengthand efliciency, is the fact that the surface of the tube or body 20 isthe virgin metal of which the tube or body 2ll is formed withoutthinning such wall or otherwise impairing its strength and efliciency.

When the strip I0 is bent and conformed helicallyabout and to thesurface of the tube or body 20,-all of the operations hereinbeforestated are preferably performed progressively throughout the wholelength or desired length of the tube or body 20; and such operationspreferably are in successive stages until the desired conformation ofthe inner edge of the strip Ill and the outer surface of its flattenedprojections l4, 2|, are of the desired conformation with th surface ofthe tube or body 20.

When the strip I0 is formed in a plurality of rings about the tube orbody 20 the meeting ends of the strip III are severed or may bepermitted to slightly overlap.

When the strip or strips l0 surround the tube or body 20 either in aring or by helical convolutions, it will ordinarily be necessary only tosolder or otherwise secure such strip to tube or body 20 only at oradjacent their opposite ends because the inner edge of the strip orstrips I0 is continuously in firm engagement with the surface of thetube or body 20.

Further advantages arising from said construction are that the coldworking of the edge of the strip or strips Ill adapted to engage thesurface of the tube or body l0 increases the thermal conductivitybetween the tube or body 20 and the strip Ill; also that the feet orlateral projections 2| of the strip or strips Ill increase not only thethermal conductivity between the tube or body 20 and each strip [0 butalso substantially increase the rigidity of each strip II) as well asits stability and resistance to deformation as well as lateral bendingrelative to the tube or body 20. and resistance to deformation orlateral bending is of great advantage due to the fact that if the spacesbetween the strips l0 forming ribs or fins Illa upon the finishedproduct be un-uniformly spaced apart or laterally bent into contact witheach other, the heat exchanging efficiency of the product isproportionately impaired, besides rendering the finished productun-uniform and/or unpleasing in appearance. The accomplishment of theseobjects even with thinner, lighter, and to such extent cheaper materialfor the strips l0, lends greater importance to the means by which suchobjects are accomplished because otherwise the thinner, wider strips H]in the finished" product would be more liable to distortion and lateralbending even with ordinary handling. Furthermore, the increased lateralsupport for the high standing ribs or fins formed of the strip or stripslllas well as the greater heat exchanging contact of such ribs or fins1011 with the tube or body 20, afforded by the projections 2l extendingalternately from opposite sides, does not impair appreciably the volumeof the heat exchanger space between the ribs or fins.

The preferred construction and'arrangement of the teeth l3 of wheel [2,with their function, will now be described. A plurality of adjacentteeth I4 have their outer surfaces beveled, as shown in Fig. 1a. Theindividual teeth iii are spaced apart by bevelled notches. These notchesare of uniform diameter at their bottoms while the ridges of the teethl3 between the notches have their outer surfaces bevelled and uniformlyThis increased stability teeth l3 thus alternate in the direction oftheir bevelsthroughout the periphery ,of wheel I2. When such bevelled.teeth It engage the edge of strip l projecting from the holder H thestrip "III will be drawn through the groove in holder 'H by the rotationof wheel l2 and the embedment of teeth It in the adjacent edge of stripI II. This embedding of the bevelled teeth l3 into the edge of strip l0causes alternating series of oppositely bevelled notches to be formed inthe adjacent edge of strip Hi. In the formation of such'notches themetal of strip l0 between such notches is displaced laterally of thenormal thickness of the strip ID in a direction away from the highpoints of the series of teeth l3 of wheel l2 which formed the notches inthe edge of strip III. This results in alternate projections uponopposite sides of the strip i3 which ultimately become the feet 2|.

As the thus formed notches l in the edge of strip l0 emerge from wheell2 they are progressively engaged, and substantially flattened by thesurfaces l9, l8, of the foot II. This engagement also tends to increasethe extent of alternate lateral projection from the sides, of strip ll)of the projections II. From support ll, wheel I!) and foot H, the stripin progresses to the point where the flat strip l0 (one of whose edgeshas been cold worked as heretofore stated) is bent edgewise about thetube or heat exchanger element 20 with said cold worked edge of stripIII in contact with the outer surface of tube or element 20. In thecourseof the helical bending of strip l0 about the tube or element 20the initial lateral projections formed upon an edge of strip in by thewheel i2 and foot l'l heretofore described'are progressively transformedinto lateral projecting feet 2| on opposite sides of the inner edge of'the helically coiled 'rib or fin. Suchv feet 2| are formed inprogressive stages illustrated-in the order 'of their progression inFigs. 3, 3a, 4, 4a, and 5, 5a, a portion'of the .rib or fin lfla in anintermediate one of said stages being shown in a portion of the interiorof the coiled rib or fln.

Fig. 2 from whichthe tube or element. 20 has been removed in order tomore clearly illustrate In so associating the strip Ill and the tube orelement 20 and their conversion into the finished product the virginsurface of the metal of the.

tube or element 20 is not'disturbedand the strip I0 is desirably bentthereabout and the feet f2l formed in firm binding contact with thenormal surface of the tube or'element 20 without requiring any thinningor other disturbance of the wall of the tube or element 20 in thesecurement of the rib or fin, strip l0, and its integral feet 2| to andabout the tube or element 20 in strip of metal adapted to contact with aheat exchanger element, comprising forming -alterhate projections anddepressions in said edge of said strip by flowing metal of said edgefrom the area of the depressions into the area of the adjacentprojections and flattening at least the peaks of said projections bylateral displacement .of the metal from said peaks into alternateprojections from opposite sides of the strip.

v 2. The method of fabricating a heat exchange device including a memberhaving mounted thereon a strip of metal, comprisingthe steps of formingalternate projections and depressions in the edge of said stripadapted'to contact said member by flowing metal of said edge from thearea of the depressions into the areaof the .adjacent projections,flattening at least'the peaks of said projections by lateraldisplacement of the metal from said peaks into alternate projectionsfrom opposite sides of the strip and conformingthe aforesaid edge withthe lateral-projections tothe outer surface of said member whereby toprovide a firm and eflicient heat exchange con-, tact therebetween.

JOHN O. HUSE.

ALFREDJ. BER-Gt

